Comparing the performance of NH4Cl-activated carbon with standard activated carbon for humic acid adsorption from aqueous solutions

Removal of humic acids during water treatment is important because it can react readily with chlorine and produce carcinogen compounds. In this study, performance, kinetic and isotherm of humic acid (HA) adsorption onto NH4Cl-induced activated carbon (NAC) has been investigated and compared to the standard activated carbon (SAC). NAC and SAC were used as the adsorbent in the present work and adsorption experiments were performed in batch mode. Adsorption of humic acid (HA) on SAC and NAC as a function of solution initial pH (2-10), adsorbent dosage (0.1-0.4 g/L), contact time (5-70 min), and adsorbate concentration (5-20 mg/L) was investigated. NAC exhibited higher HA adsorption capacity than that of SAC and HA adsorption capacities for both decreased with increasing solution initial pH in range of 2 to 10. The HA removal efficiencies of SAC and NAC were found to increase with increasing the adsorbent dosage. The adsorption kinetics data were well fitted by pseudo-second-order equation. The mechanisms of the adsorption of HA on SAC and NAC at pH 7 may include electrostatic attraction and hydrogen bonding. The adsorption isotherm data showed that adsorption behavior of HA well fitted by Langmuir adsorption isotherm for both NAC and SAC. The maximum adsorption capacity was 93.45 and 67.57 mg/g for NAC and SAC, respectively. The results revealed that NAC has significantly removed HA from aqueous solutions compared to SAC and even many other adsorbents. Thus NAC as a cheap and more appropriate adsorbent can be used for removal of humic substances from polluted waters.